14.KongreB der Internationalen Gesellschaft flir Photogrammetrie
Hamburg 1980
Kommission Nr . IV
Arbeitsgruppe Nr.IV-5
In vi ted Paper
K. KRAUS
Institute of Photogrammetry
Technical University of Vienna
GuBhausstraBe 27-29
A-1040 V i e n n a
RECENT TRENDS OF THE PRODUCTION OF
ORTHOPHOTOS AND STEREOORTHOPHOTOS
SUMMARY
International trends in production and application of orthophoto maps are
systematized on the basis of trends in aerial photography in West Germany
(increasing number of flights, predominance of scales larger than
1:20 000, growing application of color and color infrared photography,
as well as of scanners). Trends in orthophotography are derived on the basis
of the Austrian practice (application of two different image materials for
data acquisition and for image projection, edition of the Aerial Photo Map
1:10 000, color infrared orthophotos as basis for an environmental cadastre,
and so on). Experiences with stereo-orthophotos are treated in a special
section. The STEREOGRAPH for compiling stereo-orthophotos has been described
in the hope that it would facilitate the application of stereo-orthophotos
in other disciplines. Finally, on producing large format orthophotos of
scanner images is reported.
ZUSAMMENFASSUNG
Ausgehend von den gegenwartigen Trends in der Luftaufnahme in der
Bundesrepublik Deutschland (steigende Anzahl von Bildflugen, Dominanz der
BildmaBstabe groBer 1:20 000, steigende Verwendung von Farbfilmen und
Farbinfrarotfilmen sowie von Scannern) werden die international gesammelten
Erfahrungen mit Orthophotokarten mitgeteilt und daran anschlieBend die in
Osterreich erkennbaren Trends in der Orthophotographie (unterschiedliches
Bildmaterial flir die Datenerfassung und flir die Umbildung, Herausgabe der
Luftbildkarte 1:10 000, Farbinfrarot-Orthophotos als Basis eines
"Umwel tkatasters" etc.) zusammengefaBt. Den bisherigen Erfahrungen mit
Stereoorthophotos ist ein eigenes Kapitel gewidmet. Zur Betrachtung
und Auswertung der Stereoorthophotos wird der ROST-STEREOGRAPH in der
Hoffnung vorgestellt, damit eine groBere Verwendung der Stereoorthophotos
bei anderen Disziplinen zu stimulieren. AbschlieBend wird auf die Herstellung
von groBformatigen Orthophotos aus Scanner-Aufnahmen eingegangen.
581
1.
PRELIMINARY REMARKS
The production of orthophotos and stereo-orthophotos start with aerial
photography. Therefore, it will be appropriate to consider first, recent
trends of aerial photography, and to treat trends of the production of
orthophotos and stereo-orthophotos afterwards.
2.
TRENDS OF AERIAL PHOTOGRAPHY
As a gesture towards the host country of this 14th Congress, aerial
photography in West Germany is analyzed here: trends derived from this
example are representative for many other countries of the world.
Aerial photography in West Germany is systematrically registered since
1954 by the Institut of Applied Geodesy (IFAG) in Frankfurt. Based on
these records, and on private information from Prof. H. Schmidt-Falkenberg,
the following trends can be derived:
a)
the area covered by aerial photography tends to be larger with
each year. In each of the recent years, there has been covered
an aerea of more than 100 000 km2, corresponding to about 50%
of the aerea of the entire country. The corresponding percentage
in 1967 was 14, and in 1957 just 7.
b)
Large scale aerial photography is predominant: some 60% of the yearly
coverage (about 60 000 km2) is flown in scales larger than 1:20 000.
c)
While black-and-white photography remains prevalent, there is a growing
tendency toward the application of other photographic materials.
Color aerial photography has been first applied in 1959, and color infrared
photography in 1967 . Today, about 10% of aerial photography projects
(not of coverage) are using color films, and 3% are using color
infrared materials.
d)
Only about 60% of aerial photographs are used for determining coordinates
of points or for creating line maps. The remaining 40% are converted
into orthophotos or applied in photo interpretation.
e)
Beside conventional aerial cameras, scanners are applied since 1972.
In 1976, for example, an area of 4. 290 km2 has been covered by scanner
images, and in 1979 - 1580 krn2.
Environmental protection is the major direct or indirect course for
growing activities in aerial photography, and for recent trends toward methods
yielding more rigorous and complex characteristics of the natural and cultural
environment. Elementary needs of the population have been satisfied by the
great technical and social achievements of modern industrial civilisation,
and now there is a spreading consciousness of the need for man to be a partner
rather then a tyrant of nature. This ecologically motivated point of view
is widely expressed by demanding
all engineering to go along with environmental protection
a more general resource management and control
the state of environment, and all changes in it to be regularly
monitored.
All these demands are hardly managable without the modern techniques
of aerial photography and photogrammetric compilation.
587
3.
ORTHOPHOTO MAP AND/OR LINEMAP
The production of orthophotos, or of orthophotos with cartographic elements
added (especially of contour lines) - in other words the production of
orthophoto maps - can be considered as one of the photogrammetric compilation
techniques. This techniques has been made more appealing by co11siderable
advancements of recent years concerning both the equipment and the methods
applied. The chairman of the working group IV-5, Mr. D.. I. Glendinning,
has shown on the basis of his inquiry via questionnaires, that 56% of
orthophoto manufacturers have expanded their orthophoto equipment during
the years 1976 to 1980. Of these manufacturers, 26% are private or governmental
organizations that started orthophoto production for the first time. Some of
the other results of the inquiry mentioned show that most orthophotos and
orthophoto maps are produced in scales 1:2000 to 1:12 000.
To the question how far orthophoto maps are accepted in our days, let me
quote some authors from the Proceedings of the International Symposium of
the Commission IV in Ottawa, 1978:
R. R. CHAMARD, U.S. Forest Service (p.54): The orthophoto is a layer of
the Primary Base. It is an important layer, especially so, for the various
National Forest management specialists. To have a photographic image of the
land cover is better than any line map by itself. Combining various layers
or plates of the line map with orthophotos is very useful and of high demand.
K. J. LESTER, South African Survey (p.252): It is perhaps appropriate to
pose the question: Why use an orthophoto to revise a line map? Should the
orthophoto not in fact replace the line map? Many cogent reasons could be
stated in favour of either series. . .. Serious consideration is being given
to publishing the orthophoto in monochrome on the reverse side of the line
map.
G. E. BELLING, Photosurveys Ltd., South Africa (p.282): These orthophoto
maps 1:2 000 -enhanced with cadastral and contour information- provided
the basic data for rout examination, evaluation and selection and in the opinion
of the user engineers were far more suitable than the previously used line
mapping. Orthophoto strip mapping has since become standard procedure for
almost all projects relating to railroad planning and desing in South Africa.
P.A. BATES-BROWNSWORD, Australian Army (p.513): The enhanced orthophoto map
has been well received by the user.
S. DEQUAL, Professor of Surveying in Torino (Italy) (p.525): There are
numerous reasons for the slowness in the production of traditional cartography. In this situation the Marche region has decided to use the
orthophoto technique for its cartography, taking care, moreover, that each
phase of the productive process is automated to the maximum.
R. B. SOUTHARD, U. S. Geological Survey (p.601): Orthophotoquads have proved
useful as map substitutes in unmapped areas, as important time-saving aids
in photorevision and stereocompilation, and as multipurpose cartographic
bases for Federal, State,and private agencies concerned with land-use
planning and natural-resource inventories. Developments in orthophoto
instrumentation, improved quality, and digital data applications have led
the U.S. Geological Survey to make orthophotomapping and digital terrain
data acquisition a significant part of the National Mapping Program.
583
I . F . G. WHITTINGTON , Royal Australian Survey (p . 629) : The urban
orthophoto map provides an economical large scale topographic map
in areas where no other suitable mapping exists .
On the other hand, one finds similarly striking opinions in favour of
line maps . Line maps , especially in smaller scales , are renowned products
of our profession . There should and -vdl l not be changed anything in this
respect . For the future, I expect orthophoto maps and line maps both to
be applied , each there where it suits the specific purpose better . In
critical cases , however , orthophoto maps will more often be the choise,
they being manifold cheaper than line maps are ( see , e . g . ) W. H. Young
and D. M. Isbell , p . 348 of the mentioned Proceedings of Commission IV ,
Ottawa 1978) .
4.
NOTICABLE TRENDS IN AUSTRIA
Austrian orthophoto manufacturers are amoung those 26% of Mr . Glendinning ' s
inquiry who first introduced orthophoto production in or past 1976 (with
the exception of some small contracts for foreign firms) . An Avioplan OR 1
/13/ is used for orthophoto projection . Data recorded on some 10
stereocompiling instruments is processed by the program package SORA- OF
/9 , 10/ . Trends of these four years of production will be representati ve
in the first line for countries similar to Austria . First technical trends
will be treated , and then those of application .
a)
Most frequently, there is used one aerial photography for the projection ,
and another one for data acquisition .
photography for the purpose of
data acquisition
projection
date
some existing coverage
from the archives
fresh photography flown shortly
before projection time
film sort
black-and - white
corresponding to the purpose of
orthophotos (e . g . color infrared)
optics
wide angle
focal length as long as possible
overlap
60%
if there is certainty that this
photography will not be stereoscopically compiled : 20%
photo scale
a) 1 : 30 000
a) 1 : 30 000 to 1 : 15 000
for orthophotos
1 : 10 000 to 1: 5 000
b) 1 : 15 000
b) 1 : 15 000 to 1 : 8 000
for orthophotos
1 : 5 000 to 1 : 2 000
584
b)
If there is freedom of choice in this respect, there is a tendency
of choosing larger formats of orthophotos than that of the line map
of the same scale . E .g. the state Steiermark is producing orthophoto
maps 1:5 000 of format 60 x 60 cm2, out of a photography 1:20 000 /8/ .
c)
As opposed to their importance in West Germany, color photographs
do not play any remarkable role in Austria. On the other hand, there
is produced a relatively large amount of color infrared orthophotos.
Their share is expected to grow still considerably larger in the
coming years .
d)
Are contour lines to be shown on the orthophoto map, they are ln
general digitized directly in stereocompiling instruments . There is,
however, a growing readiness to accept contour lines derived by
programs (e . g . by SCOP /1/) from digitized profiles and break lines,
with computational costs becoming lower, and the quality of results
growing higher .
e)
There is considerable demand for orthophoto maps with lines of equal
terrain slopes shown on them . Such lines can be derived from the
digital height model .
f)
Repeated application of the data digitized once, made it necessary to
develop a special software for archiving terrain height information .
This same software controls the archiving of aerial photography,
and that of orthophotos as well. This software is entitled TOPIAS
(Topographic Information and Archiving Software) . Detailed information
on it is to be. found in presen.ted paper-/ 5/ .
g)
Orthophoto production within the frame of program TOPIAS, SORA-OP
and SCOP is a topographic information system . In Austria, this system
is more and more regarded not only as a technically advanced one, but
as one feasible in respects of economy and of time . In this topographic
information system horizontal terrain information is represented by
the photographic image; it can be automatically compiled applying the
archived digital height model. Information on heights, in the form of
contour lines or lines of equal slope, can be derived by compitation
from these same data .
The following trends can be derived concerning application of orthophoto maps :
h)
At the Federal Department of Standards and Surveys, orthophotos of
scale 1 : 10 000 are produced for the purpose of updating line maps
1:50 000 . These same orthophotos are edited as the independent map system
"Aerial Photo Map 1 : 10 000" (At this time without contour lines) . For
this purpose, about one quarter of the territory of Austria has already
been digitized in profiles of a density 30 to 160 m. For the half of
the digitized area, orthophotos have been produced. There is considerable
demand for the completed sheets of this map .
i)
Private forester companies are gradually changing from line maps to
orthophoto maps. They generelly prefer orthophotos in scale 1 : 5 000,
partly with contour lines added .
j)
State governments prefer for their purposes -mainly for regional planningorthophoto maps 1:5 000 .
585
k)
With the financial help of the Federal Ministry of Health and
Environmental Protection , some larger cities are preparing color
infrared orthophotos 1 : 2 000 or 1 : 2 500 .
1)
Designing highways and hydro-electric plants has been accomplished
a couple of times using orthophoto maps . These having been successes ,
one can expect such applications to become a clear trend in the future .
m)
Finally, agriculture, glaciology, and archeology should be mentioned
as areas where orthophotos have been - and probably will be successfully applied .
5.
STEREO-ORTHOPHOTOS
Although the first stereo-orthophotos have been produced by the National
Research Council in Ottawa as much as 13 years ago, no break through towards
wider applications has yet been achieved, as to my knowledge . At that time,
economically feasible methods and instruments were missing . Nowadays, extremely
precise stereo-orthophotos can be produced much cheaper, applying digitally
controlled orthophoto projectors /9/, or instruments of the type
Gestalt Photo Mapper II /14/ .
To a certain extent, these new capabilities have already gained practical
application . At the Institute of Photogrammetry of the Technical University
of Vienna, some hundreds of stereo-orthophotos have yet been produced for
Austrian, but in the first line for foreign contractors. The program SORA-OPS
/9/ to determine control data for the production of orthophotos and their
stereo-mates, has been sold to 5 organizations .
There are some positive reactions available . The IGN in Paris organized a
special symposium on applications of stereo-orthophotos . From the reports
published, that of E . Gras /4/ should be mentioned; he is reporting on the
application of stereo-orthophotos in designing highways . R. Finsterwalder /3/
advocates the production of topographic maps with a technology based on
stereo-orthophotos . The Federal Department of Standards and Surveys in Vienna
is experimenting with the application of stereo-orthophotos in updating
line maps .
Users of stereo - orthophotos are complaining about the missing of corresponding
devices for the compilation of stereo - orthophotos of large formats . Similar
problems are reported by Ducher /2/ in France . One can state, that a
provision of any break-through in stereo-orthophotos applications is the
availability of a corresponding instrument to compile them .
In cooperation with the ROST Co ., Vienna, the Institute of Photogrammetry
of the Technical University of Vienna developed the STEREOGRAPH (fig . 1)
for the purpose of viewing and compiling stereo-orthophotos . On the desc
of the STEREOGRAPH, there is place for an orthophoto of the maximal format
65 x 65 cm2 , and for the corresponding stereomates on both sides . With a
stereoscope rolling on parallel rails, and setting a viewing base of 38 em ,
one can view stereoscopically the entire 65 x 65 cm 2 large model in a
convenient manner . Transparent films can be illuminated through the base .
Setting the viewing base of the stereoscope to 65 em, and working with just
the orthophoto and one of its stereomates , it becomes possible to place
between them a sheet of paper or another copy of the orthophoto itself (fig . 2) .
586
..
Fig . 1:
STEREOGRAPH when observing stereo - orthophotos
I
I
Fig . 2:
STEREOGRAPH when compiling stereo - orthophotos
587
.
To compile just horizontal contents, one measuring mark can be used
on the side of the orthophoto . Its movements can be graphically recorded
with the drafting device (pencil , ink etc . ) on the sheet on the desc in
front of the operator . The version STEREOGRAPH-D 1 of the instrument is
provided with impulse generators for digitally recording the movements
of the measuring mark on some standard electronic recording equipment .
For compilation of heights, a second measuring mark can be used , and
moved along the X-axis via a micrometer .
In my opinion simple compilation of cheap orthophotos will be done, in
most cases , not by photogrammetrists but by photo interpreters of other
special lines . They are, as mentioned in section 2, the main initiators
of many projects in aerial photography . It seems natural to them, that the
negative image has to be photographically developed first . This chemical
process is, however, just half of the development ; the second half being
a geometric process consisting itself of two major tasks . The first of
these is the conversion of the distorted image into a geometrically correct
one (the orthophoto) showing geometric qualities of a map . And the second
task of this geometric development is the conversion of the same photographic
image into another one (the stereomate), for the purpose of stereoscopic
viewing and measurements . Both these tasks of the "geometric development"
are major provisions for a secure, convenient , and universal application
of information contained in aerial photographs .
6.
RECTIFYING SCANNER IMAGES
A paper dealing with next future would hardly be complete without treating
scanner images . They make up a couple of percents already , as mentioned
in section 2 . This percentage will probably grow larger in coming years .
Information gathered by scanners is generally recorded in digital form
on magnetic tapes . These records can be converted directly to photographic
images showing deformations similar to those of the aerial photographs .
A rectification of such images, i . e . converting them into orthophotos
is naturally possible . However, with regard to rapid development of digital
image processing, a direct rectifi cation of the "digital image" on the
magnetic tape is better suited for future usage . Just as conventional
aerial photographs should be interpreted after their "geometric development"
(stereo-orthophotos), so are digital images safe , convenient and universal
for interpretation purposes only after their geometric correction .
Such geometric correction of digital images means the creation of a second
magnetic tape with the pixels of the first tape rearranged. This
rearrangement yields a constant scale, and a reference to the geodetic
coordinate system . Generally, such rectified digital images have meridional
sides .
Although rectified digital images are further processed in computers, there
is a demand for converting them into (color) photographic images . In this,
large formats and round scales are generally requested .
The AUSTROPLAN Co. in Vienna succeeded in creating an instrument capable of
fulfilling the above demands /6/ . The device handles formats up to 1 x 1m2
and any requested scale (fig. 3). The software needed for controlling this
process is described in presented paper /7/ .
588
Fig . 3: Device to output digital irrages,
of the AUSTROPLAN Co . , Vienna .
In the yet most extensive project~ the rectified image (orthophoto) has
been composed of 7 somewhat overlapping strips of thermal imagery .
7.
CLOSING REMARKS
Research in optics~ physics, television and electronics is continuously
yielding new systems for image recording . Periodically,the chemical industry
succeeds i n improving photographic materials . It is the task of
photogrammetrists to bridge the gap between image recording methods, on
the one hand~ and interdisciplinary applications of these digital or
photographic images . In this ~ a major part is the transfer of originally
digital and photographic images with a distorted geometry impractical for
applications ~ into digital and photographic images with a geometry that
makes them convenient to use .
589
REFERENCES:
I 11 ASSMUS, E.: Berucksichtigung von Gelandekanten im Stuttgarter
Hohenlinienprogramm - Theorie und Ergebnisse .
Geowiss . Mitt. TU Wien, Heft 8, 1976.
I 21 DUCHER, G.: Interet de la Stereo-Orthophotographie et Possibilites
de Developpement . Symposium Commission IV,
Ottawa, 2.-6 . 10 . 1978 .
I 31 FINSTERWALDER, R.: Eine Kartierungsmethode unter Zuhilfenahme von
Stereoorthophotos .
I 41 GROS , G. :
Kartogr . Nachr . ,
511977.
Presentation de deux experiences d'exploitation des
stereo-orthophotographies, realisees avec l'I . G. N.
dans le cadre des etudes de projets routiers .
Journee Stereo-Orthophotographie, Saint-Mande,
le 20 Septembre 1977.
I 51 HAITZMANN, H. and KRAUS, K. and LOITSCH, J.: A Data Base Towards the
Digitally Controlled Production of Orthophotos .
Presented paper, Commission IV, ISP-Congress 1980 .
I 51 HRUSKA, H. : GOBI- The Large Format Color Printer for Rectification
and Image ~1osaicing . Presented paper, International
Symposium, Image Processing, TU Graz, 1977.
I 71 JANSA, J.:
Geometric Rectification of Blocks of Multispectral
Scanner Images. Presented paper, Commission III,
ISP-Congress 1980.
I 81 KITZMULLER, J .: Vorschlag flir ein landesweites Orthophoto-Operat
1 : 5 000 . Amt der Steiermarkischen Landesregierung,
Regionalplanung und Ortliche Raumplanung, LBD-1b
520 011123-1979 .
I 91 KRAUS, K. and OPTEKA, G. and LOITSCH, J . and HAITZMANN, H.:
Digitally Controlled Production of Orthophotos and
Stereoorthophotos. Photogr. Eng. and Rem. Sensing, Vol.45,
pp . 1353-1362, 1979.
1101 OTEPKA, G. and LOITSCH, J.: A Computer Program for Digitally Controlled
Production of Orthophotos . Presented paper, Commission IV,
ISP-Congress 1976.
1111 OTEPKA, G. and ZIRM, K.: Neue Wege der Basisdatenerfassung und -darstellung
fur einen Umweltkataster . Umweltschutz - Organ der osterr .
Gesellschaft fur Natur- und Umweltschutz , 211977 .
1121 SCHMIDT-FALKENBERG, H. : 25 Jahre Luftbild-Nachweis des Institutes flir
Angewandte Geodasie . Nachr. a .d . Karten- u . Vermess .Wesen,
Reihe I, H. 74, Frankfurt a . M. 1978.
1131 STEWARDSON, .P .: The Wild Avioplan OR 1 Orthophoto System . Presented
paper, Commission II, ISP-Congress 1976 .
1141 Van WIJK, M. C.: Geometrical Quality of Stereo-Orthophoto Produced from
Automatic Image Correlation Data. Photogr . Eng . and
Rem . Sensing . Vol . 45, pp . 1363-1369, 1979 .
590